The marmosets of the Brazilian Atlantic forest, the xerophytic scrub and deciduous, and semideciduous forest (caatinga) of north-eastern Brazil, and the Cerrado (bush savanna) of central Brazil were all considered by Hershkovitz (1977) to be subspecies of Callithrix jacchus.

Justification:
This species is listed as Least Concern as it is relatively widely distributed, adaptable, occurs in a number of protected areas, and because the current rate of decline is not sufficient to qualify it for a threatened category.

The Common Marmoset occurs in the scrub forest (forest patches in dry caatinga thorn scrub) and Atlantic forest of north-eastern Brazil, in the states of Alagoas, Pernambuco, Paraíba, Rio Grande do Norte, Ceará, and Piauí, Maranhão, Bahia, and possibly north-eastern Tocantins, originally extending south as far as the Rio São Francisco and its west (left) bank tributary the Rio Grande (about 11º30’S). Hershkovitz (1977) indicated that it also probably extends north-west into the state of Maranhão, to the left bank of the Rio Parnaíba and the Serra do Valentim (Hershkovitz 1977). Hershkovitz (1977) extended the distribution no further west than the middle reaches of the Rio Grande (left bank) and the upper Rio Parnaíba (right bank), with a lacuna between these points and the Rio Tocantins. Silva Jr. (1999) reported on localities in Maranhão and Piauí marking the north-western limit to its range, and determined that, as Hershkovitz (1977) had indicated, it extends to the left bank of the Rio Parnaíba, but there is a lack of information concering its occurrence or otherwise west from there into the basin of the Rio Itapecuru (Sillva Jr. 1999; unpubl. data, 2008). The Black-handed Tamarin, Saguinus niger, occurs to the west, but the easternmost locallities are in the interfluvium of the rios Mearim and Itapecuru (J. S. Silva Jr., unpubl. data, 2008). Flesher (2001) recorded C. jacchus in the Serra das Mangabeiras at the headwaters of the Rio Parnaíba in Piauí, approximately 10ºS, 46ºW. South of the Serra da Mangabeiras, it is possible that the Serra Geral de Goiás marks the divide with C. penicillata to the west. It has spread into numerous other regions as a result of introductions outside of its original range, south of the Rio São Francisco, accompanying the destruction and degradation of the Atlantic coastal forest and its associated ecosystems (Coimbra-Filho and Câmara 1996). Introduced and recent populations include those in the state of Sergipe and the north and north-east of Bahia, including the ‘Recóncavo da Bahia’ (Alonso et al. 1987), the state of Rio de Janeiro in south-east Brazil (Coimbra-Filho, 1984; Ruiz-Miranda et al. 2000), the Ilha de Santa Catarina in southern Brazil (Santos et al. 2005) and they are also reported to have established themselves in Buenos Aires. Alonso et al. (1987) indicated that the Recóncavo da Bahia shows a relatively narrow zone of mixing between Callithrix penicillata and C. jacchus. However, Coimbra-Filho et al. (1991/1992; Coimbra-Filho and Câmara 1996) have shown that this region was originally forested, and argued that the destruction of the natural vegetation over vast areas since the European discovery of Brazil in 1500, along with frequent and repeated introductions, certainly of C. jacchus but probably also of C. penicillata, has resulted in a confused picture of hybrids between these species and between C. penicillata and C. kuhlii (see Coimbra-Filho et al. 1993). They argued that pure C. kuhlii was the original form occurring there.

An inhabitant of gallery forest, semideciduous and deciduous scrub forest (forest patches in dry caatinga thorn scrub) and humid Atlantic forest of north-eastern Brazil. It is very adaptable, being able to live in urban parks and gardens and rural villages where it is not persecuted and has sufficient food. It has been introduced into many areas outside of its natural range, where it is able to thrive and is believed to compete with and displace other (native) marmosets.

Marmosets and tamarins are distinguished from the other monkeys of the New World by their small size, modified claws rather than nails on all digits except the big toe, the presence of two as opposed to three molar teeth in either side of each jaw, and by the occurrence of twin births. They eat fruits, flowers, nectar, plant exudates (gums, saps, latex) and animal prey (including frogs, snails, lizards, spiders and insects). Marmosets have morphological and behavioural adaptations for gouging trees trunks, branches and vines of certain species to stimulate the flow of gum, which they eat, and in some species form a notable component of the diet (Coimbra-Filho 1972; Rylands 1994). They live in extended family groups of between four and 15 individuals. Generally, only one female per group breeds during a particular breeding season.

Callithrix jacchus is a gum-feeding specialist, with gouging lower incisors to excavate holes in gum-producing trees to guarantee gum year-round. This allows it to live in very seasonal habitats, including deciduous forests and scrub in the north-east of Brazil. Associated with its specialization in gum-feeding, it defends home ranges that are much smaller than are typical of the genus: 0.72 to 5.2 ha. Castro (2003) recorded home ranges of 0.3 to 2.4 ha at Níisia Floresta National Forest, Rio Grande do Norte. Maier et al. (1982) and Alonso and Llangguth (1989) recorded home ranges of 2-5 ha in the urban district of João Pessoa, Paraíba, and Mendes Pontes and Monteiro da Cruz (1995) of 4 ha in an urban park in Recife, Pernambuco. Group sizes have been recorded to range from 2 to 15 at the Tapacurá State Ecological Station, Pernambuco (Hubrecht 1985; Scanlon et al. 1988). Usually one female breeds in each group. Twins are produced twice a year.

Although widespread and common in many localities, and even replacing other Callithrix species where it has been introduced, C. jacchus populations are declining through habitat destruction in many parts of their distribution (Mittermeier et al. 1988; Coimbra-Filho 1984). There is some limited hunting for pets.

Hershkovitz, P. 1977. Living New World monkeys (Platyrrhini), with an introduction to Primates. University of Chicago Press, Chicago, USA.

Hubrecht, R. C. 1985. Home range size and use and territorial behavior in the common marmoset, Callithrix jacchus jacchus, at the Tapacura Field Station, Brazil. International Journal of Primatology 6: 533-550.